Some early visual problems in children

Good and focussed binocular vision is extremely important for children. Impaired binocular vision could be caused by several problems. The commonest and perhaps the most important one out of these is the presence of a squint. These can be effectively treated with vision therapy and eye muscle surgery would be required only rarely.

By Dr. B.J.C.Perera

(October 08, Colombo, Sri Lanka Guardian) The ability to see is an essential requirement for all animals. In the human being it is one of the five special senses that are so important for life. The human eye begins to develop around the 5th week of embryonic life. The process of development continues and the different connections with the brain and the rest of the body are completed well before birth. Infants are born with a complete visual system but they must learn how to see.

A few minutes after birth, most infants open their eyes and start to look around at their environment. Newborns can see, but they probably don’t focus well at first, which is why their eyes may seem out of line or crossed at times during the first 2 to 3 months. Because of the puffiness of their eyelids, some infants may not be able to open their eyes wide right away. A newborn can see his mother’s face in sharp focus at birth. In fact, mother’s face is the object he or she prefers to gaze upon. By 8-10 weeks a baby should be able to visually track an object through 180° from one side of the body to the other. The visual acuity of newborns is about 20/400, way below the normal for a grown up child or an adult. The visual acuity improves rapidly and may reach 20/30 to 20/20 by the age of 2-3 years. A child’s vision will continue to develop throughout the first year of life.

Newborns have all the eye structures necessary to see but they have not learned to use them yet. Infants’ vision begins to develop at birth. Babies spend much of their early weeks and months of life learning how to see, developing such skills as focusing, teaming their eye movements, recognizing depth, developing eye-hand coordination and making spatial judgments. As the child grows, more complex skills, such as visual perception and visual motor integration develop to meet the child’s growing need to understand and interpret his world.

Most infants can focus accurately by two to three months of age. The ability to focus requires special eye muscles inside the eye to change the shape of the lens in order to form clear images. Before two months of age, an infant is capable of focusing objects both near and far, but not very well. It takes time for the eye muscles to learn how to avoid focusing "too close" or "too far away" from near or far objects. A baby usually develops the ability to track and follow a slow-moving object by three months of age. Before this time, an infant will follow large slow-moving objects with jerky motions. A three-month-old can usually track an object quite smoothly. A baby should begin to follow moving objects with the eyes and reach for things at around four months of age.

Depth perception is the ability to judge objects that are nearer or farther than other objects. Depth perception is not present at birth. It is not until the third to fifth month that the eyes are capable of working together to form a three-dimensional view of the world.

An infant’s colour vision is not as sensitive as an adult’s. It is hard to tell if babies can distinguish colours because their eyes might be attracted by the brightness, the darkness or the contrast of an object against its surroundings and not by the colour alone. By two to six weeks of age, however, a baby can distinguish two highly contrasted colours such as black and white.

An infant is born with the ability to see facial features at arm’s length but is attracted instead to high-contrast borders of objects. For example, a baby will gaze at the edge of a face or the hairline when looking at a human face. By two to three months of age, a baby will begin to notice facial features, such as the nose and mouth. By three to five months, most babies can differentiate between the mother’s face and a stranger’s face.

Children’s vision continues to develop throughout their preschool years. As toddlers, it is important for them to continue development of eye/hand/body coordination, eye teaming and depth perception. Stacking building blocks, rolling a ball back and forth, coloring, drawing, cutting, or assembling lock-together toys all help improve these important skills. Also, reading to young children is also important. They develop strong visualization skills as they "picture" the story in their minds. The demands of schoolwork can put too much stress on a child’s visual system, causing problems even if none existed before. Whereas toddlers use their eyes mostly for looking at distance, school requires children’s eyes to focus on very close, small work for hours every day. This can cause vision problems to arise. Children do not often realize that their eyes are under too much strain, and they rarely report vision problems. Because their vision is "normal" to them, they think everyone sees the way they do.

School vision screenings provide a valuable service, but children can pass a school eye chart test and still have undetected vision problems which are affecting their school work. The eye chart just checks a child’s sharpness of vision, but reading requires many other visual skills. The eye chart test cannot tell if a child’s eyes are healthy, or if he or she can track a line of print without losing his or her place, focus the eyes comfortably, or use the two eyes together for long periods of time. School vision screenings are no substitute for a complete eye examination by an optometrist.

Humans have two normal eyes and they see through binocular vision. It is a phenomenon wherein both eyes aim simultaneously at the same visual target. It is the type of vision wherein both eyes work together, simultaneously, equally and accurately, as a well coordinated team. Healthy binocular vision produces important visual perceptual skills which are part of normal human vision. The final outcome of such vision is stereoscopic vision where two separate images from the two eyes are successfully combined into one image in the brain. This is combined with depth perception to produce three dimensional images. Depth perception is an important aspect of normal, healthy vision; a result of good stereoscopic vision, the ability to visually perceive depth and three dimensional space, the ability to visually judge relative distances between objects and a perceptual skill that aids accurate movement in three-dimensional space. These are aspects of "normal" healthy vision.

Binocular vision impairment is any visual condition where binocular visual skills are inadequately developed. Binocular vision impairments often result in partial or total loss of stereoscopic vision and binocular depth perception. An important condition where the eye is obviously turned or crossed is commonly referred to with terms like "cross-eyed", "crossed-eyes", "wall-eyes", "wandering eyes" or just a plain squint. These binocular vision impairments are easily detected by others as all the observer needs to do is notice that both eyes do not aim in the same direction at all times. In addition to this, there are a whole host of rather rare conditions which cause binocular visual impairment.

In certain instances, some binocular vision impairments are not easily detected by parents, teacher or others because the turning or straying of the eye or eyes is not obvious or consistent. Some eye turns are intermittent and they come and go. Such problems are not easily noticed by the untrained observer. A binocular vision problem is likely even when an eye turn is only occasionally visible. That is why early examination whenever there is some concern about this is so important. It has been estimated that 12 out of every 100 children are affected by binocular vision disabilities.

Binocular vision impairments are more common than many people think. Just one type of binocular impairment, amblyopia or "lazy eye", affects approximately 3 per cent of the population. At least 12 per cent of the population has some type of problem with binocular vision. Plenty of people are seeing the world with only one eye. They are monocular (one-eyed), not binocular (two-eyed). Many monocular children can be rehabilitated with the help of Vision Therapy. They can become binocular and gain depth perception. Many parents of children with these visual defects are not all that well informed of all treatment options and are not gaining information about and access to Vision Therapy.

Vision therapy can be described as physical therapy for the visual system which includes the brain and eyes. Through a series of progressive therapeutic procedures such as eye exercises, patients develop or recover normal visual skills. Vision therapy is remarkably successful in rehabilitating all types of binocular vision impairments including amblyopia (lazy eye), strabismus and a whole lot of other rare visual problems. With regard to the development or recovery of binocular vision, Vision Therapy is much more successful than surgery or glasses alone.

Various scientific studies report success rates for eye muscle surgeries ranging from 30 to 80 per cent. However, success was defined as ANY long-lasting positive benefit. That is, the case was counted as a success if the patient gained ONLY cosmetic improvement (the eye appeared more straight to others), but had no improvement in visual function (the ability to use both eyes to see normally). There are disconcerting reports from parents of children who have had disappointing results following eye muscle surgery. Surgery on the eye muscles failed to restore binocular vision and, in many cases, did not even produce lasting cosmetic improvement (the eyes still didn’t look "straight" or the wandering eye went astray once again). In addition, it is most likely that one strabismus surgery often leads to another. It may be necessary to undertake multiple operations.

There are many alternatives to be considered in deciding the treatment programme for patients with binocular visual disabilities. The first alternative to be considered is what is likely to happen if nothing is done. Many patients have been advised by well-meaning doctors, friends and relatives that the child might grow out of the problem. This is practically never the case. Unless remedial action is attempted, the problem will either remain the same, become more deeply imbedded or adaptations will take place which will make treatment at a later date either more difficult or, perhaps, even impossible, to conclude successfully. The child simply does NOT grow out of the problem.

The visual system includes the brain as well as the eyes. The eyes are actual physical extensions of the brain. Visual problems are an important component of the disabilities associated with brain damage. These may also be complicated by eye movement disorders. Profoundly disabled children may suffer from a large number of visual problems but lack of communication can render it impossible to delineate specific deficiencies accurately. When such situations arise, special and age-appropriate testing of visual functions is essential. The goals of assessment are to determine the functional vision available for communication, education, navigation and other activities and to try and devise methods of enhancement and compensation to circumvent the visual problems and improve development for each individual child. This is a daunting task and needs assistance from a team of multidisciplinary practitioners to achieve the best results.

-Sri Lanka Guardian